The present invention relates to method and apparatus for effecting controlled dispersal of fluid. More particularly, the present invention relates to techniques for cyclically deflecting a fluid jet in order to achieve specific flow patterns at significantly lower pressures than possible with prior art techniques. Although the initial discussion hereinbelow relates specifically to liquid spray techniques, it will be apparent that the inventive concepts described herein are applicable also to the dispersal of other fluids, including gas, fluidized solid particles, etc.
Commerical and industrial liquid spray apparatus have heretofore utilized the so-called shear nozzle, which is a sharp-edged orifice with an outlet shaped to provide a desired spray pattern. Characteristically, a given size shear nozzle issues liquid in droplet form and in a defined spray pattern, with both droplet size and pattern configuration being dependent in part on the pressure of the liquid applied to the nozzle. Specifically, droplet size varies inversely with pressure, the rate of change being relatively small. The spray pattern, on the other hand, remains constant over a large range of pressures above a predetermined pressure, but the pattern degrades significantly at lower pressures. The pressure required to achieve a specific droplet size is also affected by the surface tension of the liquid, with a liquid of higher viscosity requiring a higher pressure than a liquid of lower viscosity to achieve reduction to a given droplet size. Likewise, the predetermined pressure above which the shear nozzle issues a constant or non-degraded spray pattern is affected by viscosity, the higher the viscosity the higher the predetermined pressure.
Different liquid spray applications have different requirements with respect to droplet size and spray pattern. For example, in the field of liquid paint spraying it is important that the droplets be sufficiently small so as not to form globules on the painted surface, generally on the order of 25 microns or less. In addition, it is important that the paint spray pattern configuration be predictable. Therefore, shear nozzles employed in paint spray applications must be operated at pressures above that which provides the maximum permissible droplet size and in the pressure range over which the spray pattern remains constant. Generally, this pressure range is higher than the pressure required to achieve the sufficiently small droplets. In comparison, agricultural sprays (i.e. pesticides, fertilizers, etc.) require that the droplet size be larger than approximately 80 microns because smaller droplets are readily carried away by air currents and thereby create pollution hazards and waste. In addition, spray pattern uniformity (i.e. uniform distribution of liquid throughout the spray pattern) is important in many agricultural spray applications. Thus, agricultural spray applications employ lower flow velocities than paint sprays. Consequently, shear nozzles for agricultural spray use are operated at pressures on the order of 50 psi to achieve the desired spray pattern whereas point spray shear nozzles are typically operated at pressures on the order of a few thousand psi. In each industry, with cost reduction as an ultimate goal, there have been many attempts to reduce the required operating pressures without sacrificing the respective droplet and spray pattern characteristics. Thus far these attempts have been unsuccessful.
It is therefore an object of the present invention to provide a method and apparatus for achieving a predictable liquid spray pattern with controlled droplet sizes at liquid operating pressures which are significantly lower than are possible with prior art methods and apparatus.
It is another object of the present invention to provide a method and apparatus for achieving a predictable liquid spray pattern, wherein substantially all droplets are below a specified size, at operating pressure well below those which are required in the prior art.
It is another object of the present invention to provide a method and apparatus for achieving a predictable liquid spray pattern, wherein substantially all droplets are above a specified size, at operating pressures well below those required in the prior art.
It is yet another object of the present invention to provide a capability for issuing a liquid spray pattern wherein liquid is uniformly distributed over the pattern and wherein substantially all of the droplets are of uniform size.
Experiments by Rayleigh and others have indicated that if an orifice is vibrated transversely of its flow axis above a specific amplitude and frequency, a liquid jet issued from that orifice breaks up into droplets of controlled periodicity and spacing. Generally, the amplitude of the vibratory translation must be at least equal to the radius of the orifice; the frequency must be equal to or greater than what shall be termed the Rayleigh frequency which is inversely related to the orifice diameter and directly related to the surface tension of the liquid. It would seem therefore, that an orifice could be vibrated transversely of its flow axis at sufficient amplitude and frequency to achieve controlled droplet formation, and at the amplitude necessary to achieve the desired spray pattern configuration. Theoretically, this is possible; but as a practical matter, achieving the vibration amplitude required for the desired spray pattern configuration at frequencies equal to or greater than the Rayleigh frequency requires a driven mechanism which of itself is more complex and expensive and requires more energy to operate than would justify changeover from the shear nozzle approach.
It is also known the liquid jets can be transversely deflected without the need for external energy sources. For example, a member in which an orifice or nozzle is defined may be reciprocated or vibrated by the energy of the operating fluid to be issued by the orifice. Typically, the reciprocating drive member would be a turbine which is driven by the liquid flowing past the turbine blades to the orifice. This approach, although not requiring any external energy, requires relatively high operating pressures to achieve the necessary reciprocation amplitude at frequencies as high or higher than the Rayleigh frequency. In addition, the fast moving mechanical components of the reciprocating mechanism are subject to failure due to constant wear and tear.
Fluidic oscillators are well known in the prior art and are widely used in many applications requiring a cyclically deflected fluid jet. Examples of fluidic oscillators may be found in U.S. Pat. Nos. 3,016,066 (Warren), 3,185,166 (Horton et al), 3,247,861 (Bauer), 3,432,102 (Turner et al), and 3,563,462 (Bauer). Operation of all fluidic oscillators is characterized by the cyclic deflection of a fluid jet without the use of mechanical moving parts; consequently, fluidic oscillators are not subject to the wear and tear which adversely affects the reliability and operation of pneumatic oscillators and reciprocating nozzles. Furthermore, since only the jet and not the entire orifice-bearing body is translated, much less energy is required to achieve jet oscillation.
The oscillators described in the aforementioned Warren and Horton et al patents are characterized by their use of boundary layer attachment (i.e. Coanda effect). Specifically, these oscillators include an interaction region with sidewalls which diverge downstream from a power nozzle. A jet issued by the power nozzle is cyclically deflected back and forth between the interaction region sidewalls, either by a portion of the jet which is fed back to effect deflection or by some other feedback force generated when the jet attaches to a sidewall. The feedback force must not only be sufficient to deflect the jet itself, but it must also overcome the boundary layer attachment of the jet to a sidewall. The result is that the oscillator cannot operate at jet pressures below a rather significant pressure level. Moreover, the attachment of the jet to the sidewalls during each half cycle of oscillation results in a "dwell" time wherein the jet is stationary. The spray pattern produced by the cyclically deflected jet contains greater concentrations of jet fluid at pattern locations corresponding to a stationary jet than at other locations. It is therefore not possible to control pattern distribution or to achieve uniformly distributed patterns, with oscillators of this type.
The oscillators described in the Turner et al and Bauer patents are characterized by what is sometimes called a flow-reversing interaction region. The sidewalls of the flow-reversing interaction region first diverge from the power nozzle and then converge toward an outlet throat in a downstream direction. When the jet flows along the left sidewall it is re-directed thereby toward the right as it egresses through the outlet throat; likewise, the right sidewall re-directs the jet toward the left. The entry of ambient fluid into the interaction region via the outlet throat is relatively restricted as compared to the Horton et al or Warren oscillators, primarily because the outlet throat is narrower relative to the egressing jet than the downstream end of the Horton et al and Warren oscillators. The limitation of ambient fluid entry reduces the boundary layer attachment to the interaction region sidewalls so that less feedback force is required to deflect the jet. Oscillation in the flow-reversing configuration is therefore possible at lower jet pressures than in the Horton et al and Warren oscillators. Because of this and other practical considerations oscillators with flow-reversing interaction regions have found numerous practical applications, such as in shower heads, lawn sprinklers, decorative fountains, industrial control equipments, etc. Nevertheless, prior art fluidic oscillators are not suitable for spray applications described supra. This is primarily due to the fact that in prior art fluidic oscillators, substantial amounts of ambient fluid or re-circulated jet fluid is ingested into the interaction region. In the Horton et al and Warren oscillators, ambient fluid enters the interaction region through the downstream end thereof and through the control passages. In the Horton et al oscillator a portion of the jet is also fed back into the interaction region. In the Bauer and Turner et al oscillators, both ambient fluid and re-circulated jet fluid are fed back into the interaction region through feedback passages. The ingestion of ambient or re-circulated jet fluid into the interaction region is undesirable for many reasons. Specifically, many spray applications require that the jet fluid not be contaminated with ambient fluid, or with jet fluid inter-mixed with ambient fluid, prior to issuance of the jet. For example, in paint spraying such ingestion tends to cause deposits of paint on the walls of the sprayer, resulting in clogging and eventual termination of flow.
Ingestion of air into the interaction region also adversely affects the spray pattern and droplet size of the liquid issued by a fluidic oscillator. Specifically, the spray pattern of liquid issued from a fluidic oscillator is generally fan-shaped. Within the fan configuration, it is desirable to provide as uniform a distribution of liquid as possible. If air is intermixed with the issued liquid, regions of air will be randomly interspersed in the fan-pattern, destroying the uniformity of liquid distribution in the pattern. In addition, the mixture of air and liquid has a different viscosity than the liquid alone, so that droplet size, which is a function of viscosity, is affected thereby.
In aerosol spray units, typically the freon or other propellant liquid is delivered from a nozzle mixed with the delivered fluid but retains its droplet form until it can explode in the ambient environment. Heretofore, fluidic elements were not practical for use with aerosol units because the low static pressure, relative to ambient, in the interaction region of the element, permitted the premature explosion of the freon droplets in the element. Similar rationale applies to the spray of fluid with a foamant-type additive; that is, premature foaming occurs in low-pressure interaction regions.
As previously mentioned, agricultural spraying applications require that droplets be larger than approximately eighty microns, a characteristic which cannot be readily achieved with prior art fluidic oscillators. Specifically, in prior art oscillators the sweeping liquid jet impinges on opposite walls of an outlet region such that the side of the jet experiences a shearing effect along the wall. The shearing in turn produces many extremely small droplets, called "fines", which are considerably smaller than the permissible droplet size.
Another disadvantage of prior art fluidic oscillators relates to their size. As indicated in the aforementioned U.S. Pat. No. 3,563,462 to Bauer, the flow reversing type oscillator of the prior art does not oscillate if the interaction region length is less than approximately nineteen times the power nozzle width, or if the outlet throat is less than twice the power nozzle width. Since the power nozzle width is often dictated by the desired characteristics for the issued spray, the minimum overall dimensions of the oscillator are likewise fixed, often at a size which is impractical for the application.
A further disadvantage of prior art fluidic oscillators relates to their minimum aspect ratio, defined as the ratio of the power nozzle depth to the power nozzle width. Generally, this ratio is on the order of two and in some applications, it may be as low as one, however; at lower aspect ratios prior art oscillators have been inoperable. As a practical matter, smaller aspect ratios permit simpler and less costly manufacturing processes to be employed in fabricating the oscillator. For example, aspect ratios on the order of 0.5 or less permit the use of single-sided etching, coining, and pantomilling techniques which are difficult, if not impossible to use in manufacturing small fluidic elements having larger aspect ratios. It is desirable, therefore, to employ the smallest aspect ratio possible without impairing oscillator operation.
In many spray and other flow applications it is desirable to monitor the flow rate of a fluid without actually sampling or otherwise disturbing the fluid flow. Preferably a flow monitor for achieving this result would operate irrespective of the compressibility of the working fluid. Ideally, such apparatus would provided an indication when a certain flow rate is achieved.
It is therefore one object of the present invention to provide an improved fluidic oscillator.
It is also an object of the present invention to provide a fluidic oscillator which operates without ingesting ambient fluid or re-circulated working fluid into the interaction region.
It is another object of the present invention to provide an improved fluidic oscillator of the type having a flow-reversing interaction region, the improvements permitting the oscillator to be constructed in much smaller size than prior art oscillators of this general type.
It is another object of the present invention to provide a fluidic oscillator capable of delivering liquid spray having a uniform spray pattern.
It is still another object of the present invention to provide a fluidic oscillator capable of delivering a liquid spray made up of droplet of uniform size.
It is yet another object of the present invention to provide an improved fluidic oscillator through which the flow rate can be monitored without employing flow or pressure sensors to disturb the flow.
It is another object of the present invention to provide a fluidic oscillator capable of operating with gaseous, liquid or fluidized solid working fluids in either a gaseous or liquid environment.
It is another object of the present invention to provide an improved fluidic oscillator capable of delivering a spray pattern of fluidized solid particles which are uniformly distributed for processing.
It is another object of the present invention to provide a personal massaging apparatus employing the fluidic oscillator.
It is still another object of the present invention to provide a paint spray apparatus employing a fluidic oscillator. It is another object of the present invention to provide an agricultural spray apparatus employing a fluidic oscillator.
It is another object of the present invention to provide a portable personal spray apparatus employing the fluidic oscillator of the present invention.